Apparatus for determining the surface abrasiveness of a paper machine web

ABSTRACT

A method and apparatus is described for obtaining a quantitative indication of paper web abrasiveness as the web subject of the test is in transit through the production machine. Test specimens of thin, sheet metal shim stock are held in light bearing pressure contact against the dry, finished or nearly finished web for a measured increment of web length. The measured quantity of specimen material lost to the measured quantity of passing web will yield a quotient indicative of the relative abrasiveness of the subject web.

BACKGROUND OF THE INVENTION

1. Field Of The Invention

The present invention relates to the art of papermaking and moreparticularly, to techniques for quantitatively monitoring the webcharacteristic of abrasiveness.

2. Description Of The Prior Art

There are many paper converting operations having a high degree ofsensitivity to the abrasive characteristic of paper. For example,decorative laminates made with multiple layers of phenolic impregnatedkraft paper are machined to final shape with steel cutting tools whichmay be rapidly dulled. Another example is corrugating medium whichabrades away the flutes of corrugating rolls in the primarymanufacturing step of corrugated board.

These, and other manufacturing difficulties arising from paperabrasiveness are noted in detail by the publications of George E. Powerfound in TAPPI Vol. 57, No. 2, February, 1974 at page 95 and ForestProducts Journal Vol. 24, No. 1, January, 1974 at page 40.

The abrasive characteristic of paper is due to the silica contentthereof. Such silica originates as sand, grit and clay contaminatescombined with the raw wood furnish from which the paper pulp is made.The caustic wood digestion process has little or no effect on thecontaminates and once combined in the pulp flow stream are extremelydifficult to remove. By additional processing such as multiple passesthrough centrifugal cleaners, such silica content may be significantlyreduced. However, it would be prohibitive to process all the pulpproduced by a typical two hundred and fifty ton per day pulp millthrough cascades of centrifugal cleaners, Moreover, in any given pulpmill, an excessive presence of silica recurs only sporadically.Consequently, tests have been developed by the trade to quantify theabrasive result of silica contained in paper.

The most widely accepted paper abrasiveness test was developed by TheInstitute Of Paper Chemistry in Appleton, Wisconsin and reported in apaper of restricted dissemination for Project 2696-18 dated Oct. 5,1976. Basically, this test involves the use of accurately weighed metalfoil specimens (brass and steel) attached to the surface of arotationally fixed cylinder. Over this foil clad cylinder at anapproximately 170° wrap angle is drawn a two thousand foot length oftwelve inch wide paper web sample. Such drawing is performed at acarefully controlled tensile force. Upon traverse of the sample length,the foil specimen is removed and weighed again for determination ofmaterial loss. The magnitude of such weight loss is directly attributedto the abrasiveness of the paper sample.

Although the results of this abrasiveness test are widely accepted asaccurate and reliable, it will be noted that elaborate laboratoryfixtures are required for an off-machine test having the inherentdisadvantage of long delay times between the moment of web issue fromthe production machine and identification of a characteristic whichultimately relates back to the pulp from which the paper web was laid.

To rectify or at least reduce this informational hiatus, what is neededby the industry is an on-line test of the paper web as it is beingformed to determine immediately if the abrasive quality of the paper soproduced is increasing so that timely corrective measures may be taken.

It is therefore, an object of the present invention to teach a testprocedure for determination of abrasive quality and an apparatus forconveniently performing such a test quickly while the web is stillwithin the papermachine.

SUMMARY OF THE INVENTION

To accomplish these and other objectives, the present inventioncomprises an apparatus for engaging an accurately weighed metallic sheetspecimen with the dry, finished, or nearly finished paper web stillwithin the producing papermachine. Such engagement is directed, with acarefully regulated bearing pressure, radially against one of theseveral web turning rolls following the machine dryer section.

The present apparatus also comprises a calibrated wheel linear counterto record the actual length of web passing contact with the specimen.

Upon passage of a desired production length of web in contact with theinitially weighed specimen, the specimen is withdrawn and removed fromthe apparatus for final weighing. The weight loss difference between theinitial and final specimen weights is apportioned to the total weblength or area having passing contact with the specimen to derive anabrasiveness index value.

Although the final measurement of a complete test is performedoff-machine, the weighing apparatus required for such final test issmall and relatively inexpensive, thereby permitting the weighingapparatus to be located in the immediate proximity of the subjectpapermachine. Consequently, the informational objective of the test maybe known within a few minutes or before a reel of finished paper iscompleted.

Apparatus refinements may include automatic controls to disengage thespecimen from test contact with the web upon arrival at a predeterminedweb test length. Additionally, the apparatus may be coordinated to thepapermachine operation by a signal from the web-break alarm system totemporarily withdraw the specimen from test engagement upon occurrenceof a web break and to re-engage the specimen upon restoration of webcontinuity without loss of the test length count.

BRIEF DESCRIPTION OF THE DRAWING

Relative to the drawing wherein like or similar reference charactersused throughout the several figures of the drawing designate like orsimilar elements:

FIG. 1 is a front elevational view of the present apparatus mounted inoperative position on the papermachine support frame;

FIG. 2 is an end elevational view of the present invention;

FIG. 3 is a plan view of the specimen support shoe for the presentinvention;

FIG. 4 is a sectional view of the specimen support shoe as taken alongcut lines IV--IV of FIG. 3;

FIG. 5 is a plan view of the specimen sheet;

FIG. 6 is a schematic of the pneumatic control circuit;

FIG. 7 is a schematic of the electric control circuit; and

FIG. 8 is an alternative embodiment of a test specimen.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Relative to FIGS. 1 and 2 there is shown an end portion of a turningroll 10 within the dry end section of a papermachine. Said turning roll10 is secured at the ends thereof by journal bearings 11 mounted on aprimary machine support frame column 12. The dry paper web W is coursedover an angular portion A of the turning roll 10 as the web travelingdirection is changed along the undulating web route through thepapermachine.

As a convenient mounting point, the present invention is secured to saidframe column 12 by means of a base plate 20. To the base plate aremounted four linear bearings 21 which carry a pair of guide rods 22.Jointly, the guide rods carry a carriage platform 23. Between the baseplate 20 and the carriage platform 23, a fluid cylinder motor 24 issecured by clevis joints to displace the carriage platform 23 between anextended position, as illustrated, and a retracted position.

Connected to the carriage platform 23 by mounting lugs 25 is a pivotbracket 26. This bracket 26 is driven through an angular arc betweenengagement and disengagement positions by a second fluid motor 30connected between clevis lugs 35 on the pivot bracket 26 and clevis lugs36 on the carriage platform 23.

Fluid motor 30 is comprised of two cylinder/strut sections 31/32 and33/34. Cylinder 31 is the larger of the two and has a displaced volumeand strut stroke approximately five times greater than cylinder 33.

Pivot bracket 26 is provided with two journal lugs 37 (FIGS. 3 and 4)secured to the upper bracket face by machine screws arranged to receivespacing shims between the bracket face and the respective lug bases.

The test shoe assembly 40, best illustrated by FIGS. 3 and 4, isbasically a hollow housing 41 constituting an air plenum for cooling airdischarge orifices 42. Air is supplied from an appropriate source bymeans of conduit 43. To the housing sides are secured journal rods 44 incooperative alignment with lugs 37. Locking jack screws 38 threadedthrough the pivot bracket face secure an angular position of the shoeassembly 40 about the axis of journal rods 44.

The saddle face 45 of the shoe assembly is arced by a radius less thanthe cooperative turning roll 10 radius so as to provide a mid-space gap46 between the saddle face 45 and a thin (0.015 inch) spring steel shimplate 47. Both ends of the shim plate 47 are secured to respective endsof assembly housing 41 by clamping bars 48.

To secure a test specimen 60 in position on the shoe 40 for the durationof a test interim, a specimen clamping assembly is provided havingclamping bars 51 and 52 disposed across opposite housing ends. Suchclamp bars 51 and 52 are tied together by a pair of clamp rods 53extended through the housing 41 plenum within sealing channels 54. A nut55 secures the clamping bar 51 to the rod 53 at one end thereof whereasa toggle-type compression clamp 50 secures the clamping bar 52 at theother end of the rod 53.

Between the rods 53 along the end faces of the housing 41 are providedcrimping rods 56. A corresponding channel 57 is cut along the clampingface of clamp bars 51 and 52.

From the rotationally leading end face of housing 41 (relative to therotational direction of turning roll 10) specimen alignment rods 58projecting from the center of crimping rod 56 are provided. The FIG. 5plan illustration of a representative specimen 60 in the new, un-crimpedcondition show apertures 61 punched into the face of the specimen ofcooperative size and span to receive the alignment rods 58.

Most shim stock grades of sheet steel, copper and brass are suitable astest specimens 60 although the softer materials are preferred due to thegreater quantity of base material abraded away per unit of linearcontact with the running web W thereby reducing the elapsed test time.One particularly useful specimen 60 construction has been toelectroplate 5 mil yellow brass shim stock with a half-mil cladding ofcopper. The visual contrast arising from the abraded removal of portionsof the copper, will provide a rapid, qualitative indication of the paperabrasiveness when compared by experience to the relevant quantity ofpassing web.

To measure such linear quantities of web contact, a calibrated wheel 70drive of 1 foot circumference, for a signal pulse generator 71 issecured to the pivot bracket 26, FIG. 1. Positional alignment of thewheel 70 provides surface drive contact with the turning roll 10simultaneous with test contact of the specimen 60. Electrical pulsesfrom the signal generator 71 actuate a digital counter and visualdisplay not shown. To further regulate the bearing pressure of thecalibrated wheel 70, the spindle thereof is resiliently suspendedindependently of the pivot bracket 26. This expedient addresses theaccuracy and long-lived reliability of the instrument.

Engagement and disengagement control over the present invention may beentirely manual or automated as desired. In general, the operationsequence first requires air pressure admission to the horizontal shiftmotor 24 to extend the carriage and shoe assemblies into alignment withthe web W. Upon such alignment, the lower cylinder 31 of vertical motor30 is charged to swing the pivot bracket 26 and shoe assembly 40 intonear proximity of the running web W. Final engagement of the testspecimen with the web is motivated by a low pressure charge of the uppercylinder 33 portion of the vertical motor 30.

The pressure and volume distinction between upper and lower cylinders 33and 31 provides distinctive spring rates in series along the column axisof motor 30. The low pressure of upper cylinder 33 translates a softengagement force to the shoe 40 and test specimen 60. Simultaneouslyhowever, the small volume of the upper cylinder 33 provides high springrate resilience to the contact force bias.

On a typical application, the lower cylinder 31 will be charged withapproximately 60 psig whereas upper cylinder 33 will be charged withapproximately 30 psig.

Relevant to the magnitude of contact pressure exerted by the uppercylinder 33 is the degree of self-energization as the phenomenon isknown to the shoe brake art. Such self-energization is dictated,in-part, by the location of the pivot bracket 26 swing axis relative tothe turning roll 10 axis and the arcuate contact angle of the testspecimen 60. These parameters are normally distinctive to specificinstallations but are extremely important to the maintenance of correctspecimen contact pressure.

Final engagement of the test specimen 60 with the web simultaneouslyengages the calibrated wheel 70 to record the linear quantity of webpassing the specimen 60. Consequently, it is not necessary to preciselytime the specimen contact with the web for calculation of the webcontact length from known machine speeds which may vary greatly over anelapsed test interim.

An automatically controlled unit may be constructed to disengage thespecimen 60 from the web upon arrival at a predetermined measured weblength by reversal of the foregoing engagement sequence. Moreover, byconnection of the unit control with the papermachine web-break alarm, atest interim started before a web break may be continued after webrestoration. In this case, a controlled retraction sequence is initiatedprior to completion of the set-point footage count. Because thepreviously accumulated footage count remains, however, the testengagement sequence is initiated upon termination of the web-breakalarm. Accordingly, the test cycle is automatically restored untilcompletion of the set-point footage count whereupon the test specimen isfinally retracted from web engagement.

FIGS. 6 and 7 illustrate representative pneumatic and electronic controlcircuitry required to accomplish the aforedescribed functions.

Relative to FIG. 7, R3-C is an activation coil for prior art pulsecounting logic R3-S which responds to signals from the calibrated wheel70 pulse generator 71 to accumulate the summation of web length havingpassed the specimen 60 from the moment of engagement. Such accumulationsare compared to a set-point value for initiation of other controlsignals upon correspondence between the set-point value and theaccumulated value.

Components L1 and L2 are indicator lights to visually communicate thatthe unit power supply is energized (L1) and that the unit is operative(L2).

Start and stop switches S2 and S1 are normally open and closedrespectively. When start switch S2 is closed, the coil R2-C of a 3-pole,double throw, normally open control relay is energized to close switchesR2-S1, R2-S2 and R2-S3. Switch R2-S1 merely sustains power continuityacross the N.O. start switch S2 after release of the starting contactpressure. Switch R2-S2 sustains continuity to the coils of time delayrelays R4-C and R5-C. Similarly, switch R2-S3 sustains continuity to thecontrol position limit-switch S4 located at the end of the horizontalfluid motor 24 engagement position stroke. Closure of limit switch S4energizes control solenoid 82 to actuate the lower vertical motor 31.

Switch R1-S is a normally closed relay switch opened by energization ofcorresponding coil R1-C in circuit with counter control switch R3-S andthe paper break switch S3.

Time delay relay switches R4-S and R5-S control actuation power tosolenoids 81 and 83 to actuate the horizontal fluid motor 24 and uppervertical fluid motor 33, respectively.

The FIG. 7 electric control circuitry interfaces with the FIG. 6pneumatic control schematic illustrating 4-way, solenoid actuated,control valves 81, 82 and 83 respective to the horizontal fluid motor24, the lower cylinder 31 of the vertical motor 30 and the uppercylinder 33 of the vertical motor 30.

Specimen 60 preparation for a test requires no more than an accurateweighing of the specimen. Furthermore, since the test principal ispredicated solely on the magnitude of specimen weight loss over a knownweb length, depending on the specimen material selected and theproportional weight loss over a test interim, a particular specimen maybe used repeatedly over as many test cycles.

Upon determination of the specimen 60 weight loss, a web abrasivenessindex may be developed as a function of the ratio between weight lossand web length. A partially normalized relationship of the measuredparameters may take the form: ##EQU1##

It will be recognized that the above relation does not include a bearingpressure parameter. For Index comparisons between abrasiveness testsmade of different webs from the same machine and test instrument,bearing pressure may be assumed constant and therefore ignored in theindex computation. However, if webs from different papermachines andtest instruments are to be compared by a truly normalized index, it isimperative that the specimen bearing pressure be determined andconsidered in the Index calculation.

Specimen weighing is not the only technique whereby the presentinvention may be used. Another technique would involve a specimen 60fabricated with multiple plated laminations of visually discerniblelayers similar to that of the copper clad brass technique previouslydescribed. By merely counting the number of abraded layers, each havinga known thickness, over a standard web test length, a reasonablyaccurate indication of the web abrasiveness may be concluded.

Another measurement technique exploitative of the present invention isrepresented by FIG. 8 wherein a composite specimen 100 is fabricated bylaminating multiple layers of electrically conductive, soft metal foil101 separated by layers of insulation paper 102. Each foil layer 101 isprovided with connector tabs 103 and 104 on opposite ends of thespecimen 100 for electrical continuity therebetween. As an abrasivenesstest progresses electrical continuity across the foil layers willsequentially be interrupted to indicate the magnitude of materialremoval. By correlating the sequence of foil continuity interruption tothe corresponding web length, conclusions may be drawn as to theabrasiveness of the web in-transit through the machine.

Having fully described my invention other modifications and usetechniques may readily appear to those of ordinary skill in the art. Asmy invention, however,

I claim:
 1. An apparatus for determining the surface abrasiveness of apapermachine web comprising:A. a turning roll secured at the endsthereof by support bearings mounted on a papermachine dry end supportframe; B. a papermachine web coursed over an angular portion of theturning roll; C. pressure shoe means pivotally secured to said framemeans, said shoe means having specimen clamp means to confine a specimenof sacrificial sheet material in an arc conforming to the curvature ofsaid web over said turning roll; and wherein said pressure shoe meanscomprises a saddle-shaped face having an arcuate face curved about asmaller radius than the radius of said turning roll, said specimen beingsecured to span said saddle-shaped face. D. retractable resilient biasmeans between said frame means and shoe means to pivot said shoe meansbetween engagement and disengagement positions of said specimen relativeto said web.
 2. An apparatus as described by claim 1 comprising specimensupport shim means spanning said saddle face between said face and saidspecimen.
 3. An apparatus as described by claim 2 wherein said shimmeans spans said face with a radius of arc greater than said saddle faceto provide an air flow space between said saddle face and said shimmeans.
 4. Apparatus as described by claim 3 wherein air dischargeapertures are provided in said saddle face to distribute cooling airover the surface of said shim opposite from said specimen.
 5. Apparatusas described by claim 1 wherein said retractable resilient bias meanscomprises first and second co-axially aligned fluid motors havingrespective cylinders and oppositely extensible struts, the volume ofsaid first cylinder being substantially greater than the volume of saidsecond cylinder.